The disadvantages of conventional piston type engines are well known and include the vibration produced by the pistons and crank shaft in converting rectilinear motion of the piston to rotary motion of the crank shaft. Various types of rotary engines have been developed to minimize these problems and improve the overall efficiency of internal combustion engines. The present invention relates to engines employing a pivoted plate or flap which serves as the piston. U.S. Pat. No. 3,707,073 is illustrative of engines of this category. The engine shown in that patent, however, uses conventional valving to control the intake and exhaust events and hence is not an advance with respect to intake and exhaust valve construction.